Background: Self-determination is a key construct to guarantee the development of skills that allow people with disabilities to acquire control over their lives. However, people with intellectual disabilities may have premature ageing processes that make it difficult to exercise these skills. This study seeks to determine the self-determination levels of 516 ageing adults with intellectual disabilities between the ages of 45 and 86 years. Method: The data were collected with an ad hoc scale developed from the Functional Model of Self-Determination. Findings: The results show that competencies related to self-advocacy and self-knowledge greatly decreased, unlike making choices and solving problems. In addition, the severity of the disability, age, place of residence and type of support are identified as variables associated with levels of self-determination. Conclusions: There is a need to prioritise the acquisition and maintenance of skills related to self-realisation as the basis for intervention proposals in self-determination.